Trooper Limani said that drivers had said “that the weather did start to change.”
“There was some precipitation that was coming down,” he said. “I’m sure that could have played a factor but we’re so early in our investigation.”
Craig R. Shuey, chief operating officer of the Pennsylvania Turnpike Commission, said at the news conference that crews had been treating the roadway since 9 p.m. on Saturday “in a cycle that probably put them through there every hour at least.”
“So they were cycling through, dropping salt and cinder as necessary,” he said.
Eighteen people, including 12 adults and six children and teenagers, were taken to the University of Pittsburgh Medical Center Somerset, Gloria Kreps, a hospital spokeswoman, said. They were treated and later released.
Thirty-one patients, ages 7 to 52, were transported to Excela Frick Hospital in Mount Pleasant, said Tom Chakurda, a spokesman for Excela Health. Twenty-seven were treated and released.
Four patients were taken to trauma centers at UPMC Presbyterian and UPMC Children’s Hospital of Pittsburgh, Mr. Chakurda said.
Eleven patients, ages 15 to 67, were also taken to Forbes Hospital in Monroeville, Pa., where two of them were in critical condition and the others were in fair condition, said Stephanie Waite, a hospital spokeswoman.
FedEx said in a statement: “We extend our deepest condolences to the families of the individuals involved in this accident. There is no higher priority for FedEx Ground than safety, and we are cooperating fully with investigating authorities at this time.”
The National Transportation Safety Board is investigating the crash, it said on Twitter.